Instituto de Agroquímica y Tecnología de los Alimentos NOVEL ANTIMICROBIAL FILMS BASED ON ETHYLENE-VINYL ALCOHOL COPOLYMERS FOR FOOD PACKAGING APPLICATION Doctor of Philosophy Presented by: Virginia Muriel Galet Supervised by: Dr. Rafael Gavara Clemente Dra. Pilar Hernández Muñoz Valencia, Noviembre 2014 Dr. Rafael Gavara Clemente, Profesor de Investigación del Instituto de Agroquímica y Tecnología de los Alimentos del Consejo Superior de Investigaciones Científicas y Dra. Pilar Hernández Muñoz, Científica Titular del Instituto de Agroquímica y Tecnolo- gía de los Alimentos del Consejo Superior de Investigaciones Científicas. Hacen constar que: La memoria titulada “Novel antimicrobial films based on ethylene-vinyl alcohol copoly- mers for food packaging application” que presenta Dª Virginia Muriel Galet para optar al grado de Doctor por la Universidad Politécnica de Valencia, ha sido realizada en el Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC) bajo su dirección y que reúne las condiciones para ser defendida por su autora. Valencia, 3 de noviembre 2014 Fdo. Dr. Rafael Gavara Clemente Fdo. Dra. Pilar Hernández-Muñoz A mis padres, Javier y Carmina ACKNOWLEDGEMENTS Me gustaría expresar mis más sinceros agradecimientos a mis directores de Tesis, Dr. Rafael Gavara y Dra. Pilar Hernández por ofrecerme esta gran oportunidad. Muchas gracias por vuestras enseñanzas, dedicación, apoyo y sobre todo por vuestra cercanía, siempre me he sentido muy afortunada de formar parte de vuestro equipo. Agradezco también al Dr. Ramón Catalá todo su tiempo, ha sido un placer las conversaciones, y las orientaciones que he recibido. Con especial cariño a la Dra. Gracia López Carballo por su tiempo y esfuerzo, por transmi- tirme toda su pasión y entusiasmo. Gracias a “Goddard Research Group” y a todos mis compañeros de la Universidad de Mas- sachusetts y al “Institute for Sustainability & Innovation” de la Universidad de Victoria. Ha sido una experiencia inolvidable poder realizar estancias con vosotros. A todos mis compañeros, los que estáis y los que ya os marchasteis, por vuestra acogida, disponibilidad, por compartir conmigo conocimientos y muy buenos momentos. A mis vecinas de laboratorio y a cada una de las personas de este centro que han compartido conmigo esta etapa de la vida. Gracias a Pablo Lacruz por un trabajo de maquetación fabuloso. A todos mis amigos por estar siempre ahí. A mis hermanos, Darío y Adelaida, con los que siempre cuento. A Carlos, por el ánimo constante. Por último y en especial, a mis padres, gracias por transmitirme vuestros valores y por enseñarme a luchar por aquello que merece la pena, por ser un ejemplo profesional y personal para mí. TABLE OF CONTENTS ACKNOWLEDGEMETS........................................................................................................... 7 ABSTRACT ................................................................................................................................. 11 1. INTRODUCTION .................................................................................................................. 17 1.1. Antimicrobial active packaging .................................................................................... 18 1.2. Antimicrobial agents ........................................................................................................ 22 1.2.1. Essential oils .................................................................................................................... 22 1.2.2. Ethyl lauroyl arginate (LAE) ....................................................................................... 24 1.2.3. Epsilon-polylysine (EPL) .............................................................................................. 24 1.2.4. Green tea extract (GTE) ................................................................................................ 25 1.2.5. Lysozyme .......................................................................................................................... 26 1.3. Polymers used in antimicrobial active packaging ................................................... 27 1.3.1. Ethylene vinyl alcohol (EVOH) .................................................................................. 28 1.4. Active packaging legislation .......................................................................................... 29 2. OBJETIVES ............................................................................................................................. 37 3. CHAPTERS ............................................................................................................................. 39 3.1. Chapter I .............................................................................................................................. 41 Article 1 ....................................................................................................................................... 43 Article 2 ....................................................................................................................................... 61 3.2. Chapter II ............................................................................................................................. 75 Article 3 ....................................................................................................................................... 77 Article 4 ....................................................................................................................................... 91 Article 5 ....................................................................................................................................... 107 Article 6 ....................................................................................................................................... 123 3.3. Chapter III ........................................................................................................................... 143 Article 7 ....................................................................................................................................... 145 3.4. Chapter IV .......................................................................................................................... 161 Article 8 ....................................................................................................................................... 163 4. GENERAL DISCUSSION .................................................................................................... 179 5. CONCLUSIONS .................................................................................................................... 191 11 ABSTRACT This PhD dissertation thesis has been focus on the development and characterization of antimicrobial packaging films based on the incorporation in the polymer matrix or on the attachment to the film surface of naturally occurring antimicrobial compounds with the purpose of inhibiting the proliferation of microorganisms and extend the microbio- logical shelf life of packaged food products. The studied active films are based on the use of ethylene vinyl copolymers (EVOH) contai- ning 29% (EVOH29) or 44% (EVOH44) molar percentage of ethylene as polymeric vehicle for the incorporation of several antimicrobial compounds -oregano essential oil (OEO), citral, ethyl lauroyl arginate (LAE), epsilon-polylysine (EPL), green tea extract (GTE) and lysozyme. These antimicrobial agents have been incorporated in the film-forming solu- tion or immobilized to the film surface by covalent bonding. Prior to the preparation of the active films, the antimicrobial activity of the selected com- pounds against selected microorganism was demonstrated, confirming that they could be good candidates to be used as preservatives for active food packaging applications, and an alternative to synthetic additives. The effect of the incorporation of the antimicro- bial agents on relevant functional properties of the developed EVOH films was studied. In general, the polymer properties as materials for food packaging were not relevantly affected. In order to evaluate the potential of EVOH matrices as sustain release systems of active compounds, the release kinetics of the active compounds from the film to different me- dia was evaluated; for that the agent release rate and extend into food simulants was monitored, and it was concluded that the agent concentration, release temperature, type of EVOH, interaction of EVOH with the food simulant, and the solubility of the active compound in the release media were the main controlling factors. EVOH matrices have also shown good properties to be used for the attachment of active molecules. In this regard, lysozyme was successfully immobilized on the film surface of EVOH. Several experiments were conducted to determine the antimicrobial properties of the resulting films in vitro against different microorganisms responsible for foodborne illness and in vivo with real foods –minimally-process salad, infant milk, surimi sticks and chicken stock- to enhance their preservation. All the materials presented a strong in vitro anti- microbial activity. Although the results obtained through in vivo tests showed activity reductions caused by food matrix effects, all materials presented significant microbial inhibition and, therefore, great potential to be used in the design of active food packaging. They can be applied as an inner coating of the packaging structure, releasing the active agent or acting by direct